A superabsorbent polymer (SAP) is a synthetic polymeric material capable of absorbing moisture from about 500 to 1000 times its own weight. Various manufacturers have denominated it as different names, such as SAM (Super Absorbency Material), AGM (Absorbent Gel Material), etc. Since such superabsorbent polymers started to be practically applied in sanitary products, now they have been widely used not only for hygiene products such as disposable diapers for children, sanitary napkins, etc., but also for water retaining soil products for gardening, water stop materials for the civil engineering and construction, sheets for raising seedling, fresh-keeping agents for food distribution fields, materials for poultice, etc.
In most cases, these superabsorbent polymers have been widely used in the field of hygienic materials such as diapers, sanitary napkins, etc. For these applications, the superabsorbent polymers are required to exhibit a high absorption rate with respect to moisture, etc., and also to exhibit an absorption rate above a predetermined level even under an external pressure.
In particular, superabsorbent polymers have been required to have higher absorption performances with recent slimness of sanitary materials such as diapers, sanitary napkins, etc. In order to allow the body fluid to rapidly spread and to be rapidly absorbed in the sanitary material at the same time, simultaneous enhancement of liquid permeability and absorption rate which are incompatible physical properties of superabsorbent polymers is emerging as an important issue.
Therefore, for simultaneous enhancement of liquid permeability and absorption rate of superabsorbent polymers, attempts have been made to improve liquid permeability of superabsorbent polymers by allowing inorganic particles such as silica, etc. to exist between the superabsorbent polymer particles.
However, when a large amount of inorganic particles is used for sufficient improvement of the liquid permeability of superabsorbent polymers, there is a problem in that the absorption rate under a pressure is lowered. Further, during processes of pulverizing and size-sorting the superabsorbent polymers, inorganic particles added to the superabsorbent polymers are separated therefrom, and thus, it is difficult to improve the liquid permeability at a desired level.
Accordingly, there is an urgent need for studies to improve the liquid permeability and absorption rate of superabsorbent polymers without the above problems.